#include<bits/stdc++.h>
using namespace std;
#define int long long
signed main() {
//	system("start https://www.lanqiao.cn/problems/12043/learning/");

	int n;
	cin >> n;

	for (int i = n; i > 0; i--) {
		if (i % 2 == 0) {
			cout << i / 2;
			break;
		}
	}

	return 0;
}
